Interactions between the nervous and immune systems are well recognized for their involvement in inflammation and in the pathology of allergic disease. However, the participation of immunocompetent cells in the regulation of synaptic transmission has only recently been recognized. Mast cell are present in large numbers in autonomic ganglia and experiments have demonstrated that histamine modulates ganglionic transmission. The specific aims of this proposal are (1) to determine the effects of endogenous activation of mast cells on neurotransmission in sympathetic and parasympathetic ganglia of the bullfrog (2) to examine the hypothesis that afferent sensory fibers can release peptides within ganglia to modulate ganglionic transmission and (3) to determine the site and mechanism for the modulation of ganglionic transmission produced by endogenous mast cell activation of sensory fiber stimulation. Extracellular and intracellular electrophysiological recordings will be made from both ganglia and mast cell degranulation assessed by morphological and biochemical measurements. These results will provide new information on the role of afferent sensory fibers in the modulation of ganglionic transmission and the role of the mast cell and endogenous peptides in producing long term changes in synaptic efficacy.